Dicamba is a selective herbicide currently used for treating e.g. corn, wheat or grassland. It kills broadleaf weeds before and after they sprout. The trivial name dicamba refers to the compound 3,6-dichloro-2-methoxybenzoic acid. The estimated global demand for dicamba in 2012 was about 12.000 metric tons per year. However, it is expected that the global demand for dicamba will increase significantly.
Dicamba is typically produced on an industrial scale from 2,5-dichlorophenol using carboxylation under Kolbe-Schmitt conditions, methylation and subsequently saponification/acidification. 2,5-Dichorophenol in turn can be obtained from 1,4-dichlorobenzene or 1,2,4-trichlorobenzene. The synthetic route via 1,4-dichlorobenzene involves nitration and subsequent diazotation, and, therefore is undesired for use on an industrial scale. The synthetic route via 1,2,4-trichlorobenzene suffers from limited availability of this starting material and from the formation of several byproducts which are formed in the synthesis of 2,5-dichlorophenol.
In order to meet the increasing market demand for compounds such as dicamba, there is a need in the art for alternative processes, involving a reduced number of steps and/or improved yield, for providing dihalogen substituted salicylic acid derivatives, especially including dicamba.
The object of the present invention is to meet the above needs. It is a further object of the present invention to implement the improved process for the synthesis of dicamba on an industrial scale. A further object of the present invention is the provision of a cost effective process for the synthesis of dicamba.
Even minor improvements in the yield in reaction sequences for obtaining dicamba would provide a tremendous benefit. For example, an improvement of yield of 1% would provide an additional annual amount 120 metric tons of dicamba.